The present invention relates to electric motor-driven valves, and particularly, to so-called canned motors preferably using a threaded armature extension to drive the valve core within a valve body and commutated by Hall-effect devices, with the windings and Hall-effect devices ordinarily being enclosed within a second, atmosphere-tight enclosure. The valve housing may comprise a two-way valve, a three-way valve, a pressure-balanced valve or a multi-port valve, as used for example in heat exchange or industrial refrigeration.
The invention also relates to supplying current to the field windings in a unique manner, resulting in a unique armature movement adapted not only to achieve maximum torque in the motor, but also to do so without any thermal overload on the field windings and bearings, whereby the motor may be operated indefinitely without failure.
Still further, and in another aspect, the invention relates to the use in such combination of ball or like bearings wherein the bearings are caged by a PTFE composition capable of furnishing relatively permanent lubrication to the bearings, and thus giving them relative immunity from conditions that would otherwise be detrimental to extended bearing life.
Electric motor-operated valves have heretofore been used in many embodiments, some of which used stem and packing sealing in conjunction with geared, shaded pole or similar motors. This type of valve had its driving motor mounted external to the valve and was connected to the valve core via a stem which incorporated various packing type sealing arrangements designed to contain the fluids within the valve enclosure. Often these sealing arrangements were the first elements to fail in service and leak due to wear, dirt, or corrosion. In some cases, these packings would leak even in new condition. The end result was leakage of fluid from the valve to the atmosphere, or of the atmosphere into the process fluid handled by the valve.
Many valve applications, particularly in the chemical, petroleum, biological, pharmaceutical, industrial refrigeration, or environmental industries cannot tolerate measurable leaks or fugitive emissions from valves in the process loop. Fluid emissions may be dangerous or toxic, or the fluids may simply be precious or sensitive to contamination, for example.
In some valve applications having small torque requirements, an improvement was made in regard to leakage by employing stepping motors mounted wholly within the valve enclosure, thus eliminating the stem and packing and its associated leakage potential. This, however, exposed the rotor, windings and associated wiring to the process fluids. Compatibility between the process fluids and the motor limited the number of fluids acceptable in valves of this type. In those limited applications wherein a stepper motor was compatible with and safe for the process fluids, significant advantages were realized: no stem or packing was required; an increased precision of positioning was available; good motor reliability was obtained at reduced cost and size; and a simple control scheme could be used.
However, entry of control and power wires into the valve-pressurized fluid envelope presented reliability and cost difficulties. Stepping motors have not been able to be applied to control ports larger than about xc2xcxe2x80x3 in diameter without internal gearing or additional commutation complexity, largely due to the inability of stepping motors to remain stalled under load, and their tendency to lose torque capability if synchronization is lost due to power losses or system forces.
Additionally, the close stator and rotor radial clearances required for small step angle stepper motors prohibits the use of a hermetic, pressure containing magnetically transparent metal can in the magnetic gap. As a practical matter, this then requires the windings to be immersed in the process fluid. This in turn limited the application to those cases wherein the fluid is compatible with the motor windings and currents in question.
A need has therefore developed for a small, compact but high torque motor capable of driving relatively large valve mechanisms to open and close valve ports, wholly or incrementally, and hold the valve mechanisms in a desired position in response to an external control signal.
Additionally, a need has developed for a motor which is able to operate in a hermetically pressure sealed condition to prevent leakage of fluids from a fluid system in which the valve operates, especially at the motor/valve interface. Further, a need has developed for a motor-operated valve for use in a fluid system that is able to operate for longer periods of time without failure when the fluid in the system is corrosive or acts as a solvent to remove material or lubricants from metal, plastic, ceramic or other surfaces that come in contact with the process fluid or with each other within the valve mechanism.
It is therefore, an object of the invention, generally stated, to provide a new and improved motor-driven valve.
Another object of the present invention is to provide a motor-operated valve having a motor producing a higher torque/lower heat relationship than has been heretofore known.
An additional object of the present invention is to provide a motor-operated valve having an operating life which is much longer than that heretofore known.
Yet another object of the invention is to provide a valve having a logical and simplified arrangement of components to provide ease and simplicity of servicing or periodic maintenance.
Still another object of the present invention is to provide a motor having a permanent magnet-containing armature or rotor within a magnetically transparent can, and which includes windings and Hall-effect devices located outside the can, with the field and the Hall-effect devices enclosed within a second can or protective closure which is also sealed to the valve body.
A further object of the present invention is to provide a sealed motor which includes only four electrical conductors passing in a sealed relation through the outermost impervious shell to operate a circuit board located between the shells containing the motor controllers therein.
A still further object of the present invention is to provide a valve core for engaging a seat in the valve body, with the valve core being made from a composite PTFE material or the like and having a valve seating surface made from a hard, wear-resistant material.
An additional object of the present invention is to provide a valve core which is adapted to reciprocate into and out of contact with an annular seat by reason of having threads therein and whose axial motion is insured by a groove and pin arrangement, and whose core is urged axially into and out of registration by a threaded shaft that is secured to said armature and which rotates therewith.
A still further object is to provide a quarter-turn type valve wherein the operator is a canned motor and the valve is turned by the combination of a threaded shaft and a wheel, scotch yoke or other mechanism having a portion attached to the valve.
Another object of the present invention is to provide a motor having a sealed or canned armature and lying within the member comprising the seal, a bearing assembly having an inner and outer race, a plurality of roller elements and a cage securing said bearing elements in position, with the cage comprising a composite PTFE or similar wear-resistant, lubricous material, whereby the bearings have a greatly increased life in relation to other bearings presented to the same environment.
Yet another object of the present invention is to provide a valve operating motor which includes inner and outer leakproof containers, which containers and other elements including the valve core, may be removed in sequence as a matter of maintenance or replacement, without disturbing the valve body.
Still another object of the present invention is to provide a method of controlling a brushless DC motor in operation, which method comprises intermittently furnishing high current pulses to the windings energizing the armature with a relatively long interval between pulses, at which time said armature is not subject to undesirable heat build-up.
A further object of the present invention is to provide a method of operating a brushless DC motor which enables said motor to provide maximum torque indefinitely, yet which is not in danger of failing from excessive thermal overload.
A still further object of the present invention is to provide a sealed motor and a valve core positioning controller wherein the armature and the valve body as well as a position sensing element are surrounded in part by the armature and whereby the armature, the driven rotary shaft and the position indicating element lie within a first sealed housing, and the position sensor, the drivers and the field for the motor lie outside the first housing.
An additional object of the present invention is to provide a motor drive arrangement which includes a rotary screw and a threaded valve core adapted to move within a valve body, with the arrangement of valve components being such that the unit may be adaptable to a number of valve arrangements, including those using single or multiple inlets/outlets.
Another object of the present invention is to provide a sealed motor and valve arrangement wherein the armature is journaled by a graphite containing bearing at one end and by the novel roller/ball bearing at the other end.
Yet another object of the present invention is to provide a motorized valve arrangement wherein the movable portion of the valve core comprises a mixing or diverting valve with a valve core in an intermediate position to allow mixing or diverting of process fluids.
Still another object of the present invention is to provide a sealed motor having a magnetically transparent enclosure for the armature, with the armature having a threaded interior stem portion with a position sensor on one end of the stem and a valve core on the other end of the stem.
The present invention achieves its other objects and advantages which are inherent therein by providing a valve body having at least one inlet and at least one outlet, a valve seat therebetween, and, in several embodiments, at least one valve core which reciprocates between open and closed positions of the valve seat and is moved between positions by threads in the core cooperating with threads on a shaft which rotates with the armature, the armature having a plurality of spaced apart permanent magnets embedded therein, a plurality of drive stator windings and Hall-effect devices commutating the windings, with a sealed, magnetically transparent can between the armature and the stator, and preferably, the entire motor being enclosed within a second housing lying outside the stator and also enclosing the drive circuitry. In other embodiments, the rotary shaft indirectly operates various types of quarter-turn valves.
The manner in which these and other objects and advantages are achieved in practice will become more apparent when reference is made to the following description of the preferred embodiments of the invention and shown in the accompanying drawings, wherein like reference numbers indicate corresponding parts throughout.